This invention relates to thread guiding wheels for use in textile machinery. The invention is applicable both to freely rotating and driven wheels. In the following the terms thread and yarn should be taken as interchangeable.
In textile machinery there are a number of applications that require a thread or yam to be guided over a wheel. One such application is in false twist texturing. In false twist texturing means are provided to heat and then cool a thread or yarn as it passes towards rotating twisting heads.
On a false twist texturing machine it is desirable to position the input feed, nip roller or apron, close to the heater entry to prevent any unsupported yarn length becoming unstable owing to the high yarn rotational speed. Unfortunately, with the increases in processing speed as equipment has improved, the heating and cooling sections of the thread line have become longer resulting in design ergonomic difficulty in fitting the input feed close to the heater entry on the more ideal straight thread line machine.
In a texturing machine thread line where feed system cannot be placed conveniently close to the heater entry it is normally required that a device is positioned at the heater entry to stop the twist passing into the free length of yarn extending upstream from the heater to the entry input feed device. Such devices are called twist stops.
Normal twist stop devices are freely rotating wheels driven by the yarn. These wheels have alternately angled inter-engaging teeth disposed about the circumference of the wheel forming a circumferential slot in which apertures in one wall of the slot receive the base of a tooth extending from the other wall of the slot. In such arrangements the yarn takes an undulating zigzag path about the teeth forcing high pressure between the teeth peaks and the yarn. This pressure stops the yam rotation. The surface finish of the peaks of these teeth is extremely critical if filament damage is to be avoided particularly with multi- and fine filament yams. For example, GB Patent No. 908112, describes a rotatable disc having at its periphery a series of radial slits whereby oppositely bent blades form a zigzag V shaped groove in which the yarn runs. Similarly in GB Patent No. 603003 a V-shaped groove is used having a series of spaced depressions or openings to obtain sufficient grip on the yarn. A similar device is shown in GB Registered Design number 895467, comprising a pair of coaxial secured discs with formed-out ribs between cut-outs on each disc, the ribs on each disc meshing with the cut outs of the other disc.
Twist stops of this type however tend to abrade the yarn filaments or even break the yarn. If a yam breaks it can wrap and get trapped in the twist stop. This can result in distortion of the twist stop during wrap removal by the machine operator so that the twist stop ceases to be an effective twist stop. To reduce these problems the ribs may be stand proud of a disc without slits or cut-outs, as described in GB Patent Number 1297097. Such ribs, or lugs, may be rounded in cross-section so as to provide for more gentle control than with the twist stops previously described. There are however difficulties in producing parts with identical ribs as regard to dimension and surface finish, not only from one twist stop to another, but also around the periphery of a single twist stop so failing to satisfactorily control the yarn sufficiently in this sensitive area. The abrading action of the yarn also wears parts rapidly because of the high contacting pressure on the teeth of the device.
Devices similar to that described above have been made in ceramic materials but it is difficult to achieve the necessary surface finish and they are very easily broken in service.
As an alternative to the above described twist stop devices there is also known a twist stop comprising of a plurality of cylindrical pins secured the periphery of a roller, which pins are alternately oppositely inclined out of the central plane of the roller to form a V-shaped, zigzag yarn path around the periphery of the twist stop. The pins can be of metal or ceramic materials, but if made in metal they are easily cut by the abrasive action of the yarn and if they are made of ceramic they are fragile and easily broken by the machine operator.
The present applicants have realised that the present complex wheels can be replaced by a simple device that is usable both for twist stops and, when used as driven wheels, as textile yam feeds.
Wheels are known which have a generally U-shaped circumferential slot in which a thread is free to move laterally in the base of the U. U.S. Pat. No. 2,642,236 discloses a yarn tensioning device in which a yarn passes over a braked pulley having a generally V-shaped groove but there is no indication that this pulley acts in any way differently from a pulley having a U-shaped groove.
In the present invention a textile machinery thread guiding wheel is provided, the wheel having a circumferential slot adapted to receive a given yam, characterised in that the circumferential slot is generally V-shaped in section, having axially opposed walls which, in a radially inwards direction, converge to a base at which the walls intersect, the sharpness of the base of the V being sufficient to grip, without additional slits cut-outs lugs or ribs, between the axially opposed walls, a part of said yarn extending about at least a part of the circumference of the wheel.
The verb grip should be taken in its ordinary English sense as meaning xe2x80x9cto hold firmly or graspxe2x80x9d.
Preferably the thread guiding wheel comprises a pair of discs, the V-shaped slot being formed by opposed surfaces at the periphery of the discs.
The V-shaped slot may be formed by the intersection of a substantially flat surface with a curved surface. The flat surface may be on a first disc and the curved surface on a second disc. The curved surface may be substantially frusto-conical.
Advantageously at least a pair of radial slots are provided intersecting the base of the V-shaped slot.